Many handheld devices, such as personal digital assistants (PDAs), wireless telephones, cellular telephones, and laptop computers, incorporate graphical displays. Because these devices operate on battery power, they are constrained to a limited time of operation based on battery drain. Some device displays may cause a drain on the battery even when the device is not fully in use. For example, the typical handheld device has a means of indicating a status, such as whether the device is on or off. Additionally, the display may provide an indication of received radio signal strength from a network, and battery charge status. Recent models of mobile telephones employ graphical displays that incorporate all or more such indications as standard regardless of whether the phone is fully powered or in stand-by mode. Because the graphical display requires battery power to maintain standard indications, the battery charge time and thus operation time of the mobile device is inconveniently reduced.
Various techniques can be used to reduce battery drain due to a device display. One such technique is to define a partial display area, such that when user input is not present for some period of time, only a portion of the display receives power.
Another technique is to reduce the color depth of the displayed pixels. Normally, for a full graphical display, several bits are utilized to define each basic spectral color per pixel. However, when a device is in a stand-by mode, it is not necessary to provide a full-color depth. In stand-by mode, a reduced number of colors could be used such that fewer bits per basic spectral color are required. This reduced number of bits reduces battery drain by lowering the power required to refresh the display.
Although techniques such as partial display and reduced color depth help reduce battery drain by the display, other elements within a handheld device associated with the display also require battery power. For example, none of the techniques address the power consumed by graphic display buffers or other similar memory elements required to maintain the display in standby mode.
Therefore, a need exists for reducing the battery drain due to other elements of the display circuitry, when the device display is in a stand-by mode or partial display mode.